Max Speed 1997 2700SCR w/single 5.7 L Engine

[azankich]

Hello,

I've owned my 1997 2700SCR with a single Mercruiser 5.7 liter engine and Alpha One outdrive for a little over a year. The performance is driving me INSANE but my boat mechanic says it is as expected. My MAX speed is 16.5 knots at 4,000 RPM (there is very little extra weight on the boat beyond two regular size people, minimal fresh water and minimal fuel). That speed isn't even on a good plane. :(

Anything above 4,000 RPM and the engine temperature spikes way above 225 degrees which scares the bejebuz out of me. It is fresh water cooled.

What speed should I be seeing at 4,000 RPM on this small single engine? The engine -and- outdrive were just serviced a month ago.

My mechanic also said that the impeller is fine and the temperature is normal when the engine is pushed that hard, although from what I read the normal operating RPM for this engine is 4400 - 4800. He also said it has the correct prop spec'd for the boat.

Suggestions? Would love to hear what speed and temp this should be at. Also can I increase the size of the heat exchanger, put a lower temp thermostat or something else because it's running so hot?

Does anyone know a good boat mechanic in Seattle that I can call and make sure my other mechanic isn't missing anything obvious?

Thank you!

[seapuppy]

welcome to the zoo....unfortunately what your saying tells me a couple of things is possible....1)the hi temps is wrong for freshwater cooled...I think your mechanic is hoping it blows up on you so he can suck the wallet dry....with that said...it should run at all speeds 4200-4800 rpm and not overheat......so...what can cause it...bad impeller...yeah..he says that it's good...but the alpha one impeller is easy to replace and will only cost under a hundred bucks to install...25bucks if you do it yourself...6 bolts and the lower unit is off.....get a maintenance book and check it out....
2)speed...alot of things can cause this....at 4k rpm you should be hitting about 25-27mph....that is after it's all trimmed out properly and on smooth water....
timing on the engine....if it's not advancing all the way to spec..then your not going to get up to wot......is the hull clean??...I'm assuming your in a lake....check the bottom for any growth...i mean any kind of growth will slow that boat down dramatically.........
prop...what prop do you have on the drive now??...I'm thinking it should be about 23" pitch...however if your not getting wot...on plane..then something is definitely not right and it should be lower...like 21" pitch.......you should be able to hit min of 38mph wot.......
now for a mechanic....I've been working with one mechanic I've known for yrs...he's about the best there is around the seattle area is Art at lake union sea ray in everett.....phone is 425-347-6000....talk to either jim on parts or dale who runs the place....all 3 guys are about the best around here....I've been going to these guys for 10 yrs....
buy them a pizza and they will totally rebuild the boat in a week.....haha...ok..just kidding.......but they are the best!!...

SP :hello:

[Dave]

I would guess that this has been checked already, but is the prop spun? That could cause slower than expected speed. But wouldn't explain the high temperatures.

Has the heat exchanger been cleaned and backflushed recently? If it has never been cleaned out since new, it could possibly have quite a build up of crude on the raw water side of the exchanger tubes. And/or some sort of obstruction.

A lower temperature thermostat won't change anything because your thermostat should be wide open as it is. The thermostat might be stuck closed though. They are pretty simple but I suppose it could happen. Something to check.

You should be able to run the engine wide open all day without overheating. Your mechanic is feeding you a line about being normal when "working that hard". All boat engines work hard. I have a 5.0 ltr and when I run wide open at 5000 RPM the temp stays about 175.